Tetramethyllead recovery



United States Patent 3,515,739 TETRAMETHYLLEAD RECOVERY Shirl E. Cook,Baton Rouge, La., and Thomas O. Sistrunk, Birmingham, Mich., assignorsto Ethyl Corporation, New York, N.Y., a corporation of Virginia NoDrawing. Continuation-impart of application Ser. No. 200,965, June 8,1962, which is a continuation-in-part of applications Ser. No. 809,609,Apr. 29, 1959, Ser. No. 41,783, July 11, 1960, Ser. No. 91,598, Feb. 27,1961, and Ser. No. 104,773, Apr. 24, 1961. This application Feb. 6,1969, Ser. No. 797,260 The portion of the term of the patent subsequentto Aug. 14, 1979, has been dedicated to the Public Int. Cl. C07f 7/26U.S. Cl. 260-437 3 Claims ABSTRACT OF THE DISCLOSURE Tetramethyllead issubjected to steam distillation while associated with a hydrocarbon suchas toluene. This enables recovery of the tetramethyllead whileprotecting it against thermal decomposition.

This application is a continuation-in-part of our co pending applicationSer. No. 200,965, filed June 8, 1962 which in turn is acontinuation-in-part of our applications Ser. No. 809,609, filed Apr.29, 1959, now U.S. 3,049,558; Ser. No. 41,783, filed July 11, 1960, nowabandoned; Ser. No. 91,598, filed Feb. '27, 1961, now abandoned; andSer. No. 104,773, filed Apr. 24, 1961, now abandoned.

This invention relates to tetramethyllead associated with a specifichydrocarbon complement which confers upon the resultant composition anunusually great re sistance against the adverse consequences of thermaldecomposition such as might occur upon exposure to heat.

According to the present invention essentially pure i.e., highlyconcentrated-tetramethyllead is stabilized against thermal decompositionduring its recovery from a reaction product mixture by associating withthe tetramethyllead from about 20 to about 45 weight percent, based onthe total weight of said composition, of a hydrocarbon having a boilingpoint at atmospheric pressure in the range of from about 90 to about 150C., said hydrocarbon being selected from the group consisting of alkanesand mononuclear aromatics containing only aromatic unsaturation. Inshort, we provide in accordance with this invention a method ofrecovering tetramethyllead by steam distillation while associated withfrom about 20 to about 45 weight percent, based on the total weight ofthe composition, of a hydrocarbon of the type just described. Thishydrocarbon can be a single material such as toluene, isooctane (i.e.,2,2,4-trimethylpentane) or other similar material. However, if desired,equally good results are obtainable by using mixtures of suchhydrocarbons so long as they possess the physical and structuralcharacteristics specified above. We especially prefer to use toluene orisooctane (i.e., 2,2,4-trimethylpentane), or a mixture of the two, sincethese particular materials are plentiful, inexpensive and very effectiveas thermal stabilizers. Moreover, both of these materials are ofconsiderable value as blending stocks in the finished gasolines forwhich the tetramethyllead concentrates find their predominant usage.

Another preferred embodiment of this invention is to use hydrocarbons asabove defined which are liquids at room temperature and at least aportion of which boils at or above 110 C. Very desirably only minorportions of such preferred hydrocarbons boil below 110 C.

Although it is most desirable to employ from about 20 to about 45 weightpercent of the various hydrocarbons described above as thermalstabilizers for the tetramethyllead, it has been found that amounts aslow as about 3,515,739 Patented June 2, 1970 ice percent give goodresults in many cases (e.g., when using toluene or isooctane).Accordingly, the invention is not intended to be limited to the preciseconcentration range specified above although it will be understood thatmarked departures from the foregoing range of the concentrations areundesirable from a number of standpoints including cost effectiveness,ease of processing, and the like. Thus, if the concentration issignificantly less than about 15 percent on a weight basis inadequatethermal stability is very likely to be encountered. Conversely if theamount of hydrocarbon liquid is substantially in excess of about 45percent on a weight basis not only is the cost excessively increased butthe resultant concentrate becomes too dilute from a storage and shipmentpoint of view. Therefore, in general, hydrocarbon concentrations rangingfrom about 20 up to about 45 weight percent are the most suitable foruse in accordance with this invention.

The above tetramethyllead-hydrocarbon compositions are preferablyprepared via the process described in our prior application Ser. No.809,609, filed Apr. 29, 1959, now U.S. 3,049,558. Thus, in effectingthis preferred mode of preparation reference should be had to thedisclosure of that application for the operating details. A particularadvantage of forming the compositions by conducting that processtechnique is that the tetramethyllead so-produced is intimatelyassociated with the thermal stabilizer complement from the time that thetetramethyllead is formed. Accordingly, the tetramethyllead iscontinuously protected against the potential ravages of thermaldecomposition not only during its formation but during all subsequenthandling and storage operations involving the resultant compositions.

The above compositions may, however, be prepared by mixing theappropriate diluent with tetramethyllead formed by other procedures. Inthis embodiment it is desirable to admix the appropriate concentrationsof the tetramethyllead and of the thermal stabilizers at an early stagein the processing operations so that the time during which thetetramethyllead is in its concentrated state is reduced to a minimum. Ineffecting this mixing operation use can be made of conventional tyms ofreaction vessels, proportioning pumps, or the like.

Excellent results flow from the unification of the present ingredientsin accordance with this invention. In the first place, the thermalstability of the tetramethyllead is markedly increased as compared withunstabilized, pure tetramethyllead itself. In fact, experiments haveshown that the thermal stability of the tetramethyllead-hydrocarboncompositions is frequently 500 times as great as the stability of puretetramethyllead. Furthermore, these compositions are improved in thermalstability characteristics in at least two respects. For one thing, theirrate of decomposition is substantially reduced as compared with the rateof decomposition of unstabilized tetramethyllead. In ad- .dition tothis, these compositions develop far less decomposition pressure thanunstabilized tetramethyllead.

The present thermal stabilizersi.e., the alkanes and mononucleararomatics containing only aromatic unsaturation as described abovearesubstantially more effective for this purpose than naphthalene andstyrene which were among the most effective thermal stabilizersheretofore known for alkyllead antiknock compounds (see U.S. Pats.2,660,591 through 2,660,596, inclusive). This is a singularly unexpectedresult since by definition the present thermal stabilizersi.e., thealkanes and the mononuclear aromatics containing only aromaticunsaturation having boiling points at atmospheric pressure in the rangeof from about to about C.-are not fused ring aromatic hydrocarbons norare they compounds characterized by possessing conventional olefinicunsaturation.

The presence of the inert hydrocarbon liquid provides a highly desirablecomponent of an antiknOck liquid,

providing a component of high antiknock value in itself and also beingitself particularly susceptible to antiknock or octane numberimprovement.

EXAMPLE I In the following operations an autoclave was employed whichwas fitted with an internal agitator and a jacket for circulating a heattransfer fluid. In addition, vapor and liquid return lines, to acondenser, provided for condensing and reflux of liquid as desired.

The autoclave was charged with monosodium lead alloy flakes in theproportion of approximately 22 pounds per cubic foot of reaction space.In addition, approxi mately percent by Weight, based upon the alloy, ofgraphite was introduced as a reaction lubricant, plus approximately 0.2percent of aluminum, as trimethylaluminum. Toluene, in the proportion ofpercent of the alloy weight, was introduced. The reactor and contentswere heated to approximately 80 C., and a feed of liquid methyl chloridewas then started at a rate of about 10 parts per minute per 100 parts ofalloy charge. Reaction occurred promptly, as shown by a furthersignificant rise in operating temperature. The pressure was also allowedto rise to 180 p.s.i.g., and at this time reflux of vapor, principallymethyl chloride, was initiated to maintain the pressure at this level.The temperature of the reaction mixture was thus controlled in the rangeof 95 to about 80 C. by variation of the degree of cooling for refluxingpurposes. The methyl chloride feed was continued until a total ofapproximately 5 8 parts by Weight per 100 parts by weight of alloycharged had been introduced, this corresponding to approximately 160percent excess of the theoretical requirement. The reaction conditionscontinued for several hours after termination of the feed, and then thetemperature stopped rising and began to drop slightly. The excesspressure was vented shortly thereafter and the autoclave contents cooledto approximately ambient temperature. The charge was then dischargedfrom the autoclave into ta pool of water in a steam distillation vessel,and the tetramethyllead and toluene were recovered in high yield.

EXAMPLE II In this operation, substantially the same procedure wasemployed as in Example I above, except that the sodium lead alloy wascharged in the proportions of about 40 pounds per cubic foot of reactionvolume. In addition, the reactor was charged with toluene in theproportions of about 10 parts per 100 parts of the alloy, andtrimethylaluminum in proportions providing about 0.2 weight percentaluminum based on the sodium lead alloy. The autoclave and contents wereheated to about 90 C., and then methyl chloride feed was initiated.Reaction started almost immediately and the pressure rose rapidly,condensation of vapor and reflux being started by condenser cooling atabout 130 pounds per square inch pressure. The bulk of the reaction wasconducted at a pressure of about 210 pounds per square inch gauge. Thetemperature during the feeding and in the reaction zone was readilycontrolled in this manner, rising in one short period to about 113 C.,but the mean temperature was about 100 C. Upon termination of thereaction, the reacted mixture was discharged from the autoclave to asteam distillaiton operation, and a yield of approximately 70-75 percentof tetramethyllead was obtained, admixed with about weight percenttoluene. The operation during the entire reaction period was smooth andreadily controlled.

EXAMPLE III In this operation the alloy was charged to an autoclave inproportions of 57 pounds per cubic foot of reaction space. In addition,and at the start of the cycle, a mixture of toluene and methyl aluminumsesquichloride catalyst was charged to the reactor, in the proportionsof 10 parts of toluene per 100 parts of alloy and methyl aluminum 4sesquichloride in the proportions of about 0.8 part based on 100 partsof alloy. Further, methyl chloride liquid, in the proportions of 94pounds per 100 parts of alloy was fed at the very start. This chargecorresponded to proportions of about 4.3 times the stoichiometricrequirements of the reaction.

The vessel was then heated by circulating hot water at C. through ajacket, while agitating the contents. The temperature was raised toabout 70 C. and reaction started smoothly and continued without anydifliculty of control, until the reaction was essentially complete. Thetemperature of the reaction mixture during this period rose from 70 to100 C., the mean temperature being 85 C. The pressure of operatingduring the reaction period was maintained at about 205 pounds per squareinch gauge.

At the termination of the reaction, the excess pressure was vented andthe autoclave charge was cooled by circulating a cooling medium in thejacket. The contents were then discharged and subjected to a steamdistillation, and a yield of about 70 percent tetramethyllead wasobtained, accompanied by toluene in a concentration of about 35 percent.

EXAMPLE IV The same procedure as employed in Example III above was usedin charging the autoclave, except that the meth-- refluxing of liquefiedvapors, at about 170 p.s.i.g. Reac-.

tion occurred very smoothly and the temperature continued to rise at areasonable rate up to as high as 118 C., the mean temperature being ator slightly above C. After several hours reaction with easy control, theautoclave and contents were cooled and excess pressure was vented. Thereacted charge was discharged and steam distilled. A high yield, of theorder of about 65 percent tetramethyllead, accompanied by about 35weight percent of toluene was recovered.

EXAMPLE V When Examples I through III are repeated, except that thetoluene is introduced in the proportionsof about 20 percent, based onthe alloy, similar results are achieved,

except that the average temperature of operation is slightly higher.

When the conditions of operation of Example IV areused, the toluene orother inert hydrocarbon should not be used in proportions significantlyabove 11 or 12 weight percent of the alloy, in order to be below thepreferred upper limit of 50 volume percent of the methyl chlorideprovided.

In addition to operation at higher concentrations of inert hydrocarbon,as exemplified above, perfectlysatisfactory results are achieved whenthe hydrocarbon is substantially reduced in concentration, asillustrated by the.

following example.

EXAMPLE VI Generally, the same procedure as described in Example I wasfollowed, the loading of the reaction zone or autoclave being about 37pounds of alloy per cubic foot. :Instead of providing toluene in theproportions of about 10 parts to parts of alloy, however, theconcentration was lowered to about only 7 parts per 100 parts of alloy.The catalyst employed was in the proportions of .44 part oftrirnethylaluminum per 100 parts of alloy. Upon raise ing thetemperature by external heating, and feeding methyl chloride in theproportions of about 1.6 times theoretical requirements, very eflicientoperation was obtained, the pressure being stabilized at 180 pounds persquare inch gauge, and the temperature rising and being controlled at amaximum level of about 110 C., and a 6 ployed in limited quantity in theabove process are highly effective in inhibiting the decomposition oftetramethyllead. The following data illustrate clearly the magnitude ofthis benefit. A series of operations were conducted in which specimensof pure tetramethyllead, or tetramethylminimum temperature of about85-90 C. After reaction, lead with defined quantities of inert liquidswere subjected the reacted m1xture was discharged and steam distilled toa procedure designed to cause decomposition, and anal a dhigh yield pg130 t1percelnt tetramlethyillead was allow measurement of the rapidityand/or severity of the ac ieve accompanie y e to u'ene emp oyedecomposition. This procedure involved inserting the If desired, theinert hydrocarbon concentration can be specimen in a closed steel vesselhaving a wire passing iiivi lfl ioli s iafififi iii? 521355 1523"? i ifi the ii h .i i -"1 erng qu e e wire was en ea e y passing e ectrrcacurrent operable. However, the best results are usually providedtherethrough. The temperature of the specimen was also when aconcentration of at least 10 pounds per 100 pounds measured. Recordingpressure devices, in some cases of of lead is used. the oscilloscopetype, were employed to provide a clear EXAMPLE VII and accurate recordof the time-pressure history. In a when Examples I through IV arerepeated, except that, series of OPGIZIUOHS of th1s character, thefollowing results instead of toluene, either 10 or percent of2,2,4-triwere Obtame methylpentane (isooctane) is substituted for thetoluene, 9 similar results are achieved, except that the temperatureInitiation Maximum Maximum ggg gg; of operation at comparable pressuresare slightly lower speclmen p pp s e t (see) than the case of theforegoing examples using toluene. Pure 105 265 1,030 About M Inaddrtron, when a low excess of methyl chloride is used, wt. percent 0 asin Example IV, the upper limit of the amount of iso- 25 fifi%%"}' j5;'gfig 1 5 165 100 50 octane should be reduced, desrrably, to not overabout /2 toluene 105 80 5 the liquid volume of the methyl chloridereactant.

Instead of pure hydrocarbon compositions, mixtures or foregQmg Showseffect of the Presence Of toluene blends can be employed, and in somecases are preferred, on improving the stability of tetramethyllead. Itis seen as shown by the following example. that an increase 1n stabilityof from 175 to .500, at least,

PLE I in improvement is realized. Similar benefits were demon- EXAM VIIstrated when the decomposition of specimens was initiated The procedureof Examples I through IV is repeated in y lgllltlqll Famed y a thefmltereaction In these p operations wherein, instead of toluene, an aromatictype 9 a slmllar p f Was used: except that the electllc solvent isemployed having an initial boiling point of wire was used to initiate athermite reaction. The thermite about 100 c. and a final boiling pointof abouit 13(31 1?. e ga p u lp se p Similar yields and ease ofoperation are attaine an t e ure 0 Over S0 t 18 tec nlque provl es avery tetramethyllead is accompanied, during steam distillation drastictest. In these experiments the effectiveness of typirecovery, by asatisfactory concentration of the solvent cal thermal stabilizers ofthis invention was directly comcomponents. Similar results are achievedin the foregoing 4O pared with the effectiveness of styrene and ofnaphthalene, operations. It is also observed that a more uniformdistritwo of the most effective alkyllead thermal stabilizers bution ofinert liquid is observed, accompanyin the heretofore known. Thus, in RunA below the composition tetramethyllead product, during the steamdistillation, than of this invention contained approximately 39 percentby is obtained when using a pure isooctane diluent material. weight oftoluene and in Run B it contained approximately 26 percent by weight ofisooctane. For comparative pur- EXAMPLE 1X 1 f 11 d poses thetetramethyllead used in Runs C and D contained The procedure followed inExamp e III is o owe approximately 31 percent by weight of styrene andapgenerally, except that an alloy containing 20 weight perproximately 26percent by weight of naphthalene, respeccent sodium is used. The chargeto the reactor consists of tively. The results of these operations wereas follows:

Decom- Initiation Maximum Maximum position Run Specimen temp. temp.pressure time (sea) A 40 g. TML+30 ml. toluene 230 360 7. 5

B 40 g. TML+20 ml. isooctane 410 25 C 40 g. TML+20 ml. styrene. 105 3351275 3 D 40 g. TML+25.9 wt. percent" 105 2, 000 0. 5

Parts From the above, it is seen that the presence of the hydro- Alloy 2carbon solvents results in improvement in the stability of Methylchlorlde g 0 from 70 to 250 times the stability of tetramethylleadToluene alone. Moreover, the thermal stability of the compositionsTrrmethylalummum 2 The quantity of methyl chloride used amounts to 1.4theories, plus a slight excess to occupy the free space in the reactionsystem. After charging these reactants, the autoclave and contents areheated to suitable temperatures to begin reaction, and the bulk of thereaction is carried out at approximately 100 C. and a pressure of aboutpounds. After completion of the reaction, the reacted mixture isdischarged and the tetramethyllead is steam distilled, a high yieldbeing accompanied by about 25 percent toluene.

One of the particular beneficial efiects of the present invention is thefact that a highly stable system is achieved and maintained. It is foundthat the inert materials emof Runs A and B was to be over 200 percent asgreat as the thermal stability of a corresponding composition whichcontained styrene as the thermal stabilizer. Furthermore, the maximumpressure produced in Runs A and B were far less than that developed inRun C. By the same token the compositions of Runs A and B were vastlysuperior from the thermal stability standpoint as compared to thecomposition composed of tetramethyllead and naphthalene used in Run D.In fact the compositions of Runs A and B had decomposition times thatwere at least 15 times as long as the decomposition time of thenaphthalene-containing composition. Moreover, the maximum pressuredeveloped was far less with the compositions of Runs A and B than it wasin the case of the naphthalene-containing composition.

Similar results are achieved when, instead of determining the rate ofdecomposition of a tetramethyllead product which has been separated fromthe other components of the reaction, a determination is made of thereacted mixture (reaction mass) prior to separation. Tests have shownthat the rate of decomposition is reduced by a factor of at least about4 and usually over 6. Hence, the tetramethyllead is stabilized duringthe reaction as well as during subsequent separation and aftersegregation of the tetramethyllead product.

The foregoing shows the great degree of improvement in stability evenwhen the specimen is subject to the severe shock of a thermite typereaction. A highly significant benefit in the present operation is thatit assures that the inert liquid is in the presence of thetetramethyllead from the moment it is synthesized and remains with, oraccompanies the product, during recovery operations. The most effectiverecovery operations involve a partial pressure operation to isolate atetramethyllead product fraction. Hence, it is of importance that thevolatility of the inert liquid be in the neighborhood or approaching thevolatility of tetramethyllead, at least with respect to some componentsthereof. Toluene, having a boiling point of 110.6" C. is ideal in thisrespect. However, commercial hydrocarbon streams, having a boiling rangewhich overlaps the normal boiling point of tetramethyllead, are quiteacceptable. These may be pairafiinic or aromatic in char-.

acter provided they possess the physical and chemical characteristicsdescribed above.

We claim:

1. In a method of recovering tetramethyllead, the improvement accordingto which the tetramethyllead is steam distilled While associated with ahydrocarbon have ing a boiling point at atmospheric pressure in therange 1 of from about to about 150 C. in amount sufiicie'nt to stabilizethe tetramethyllead against thermal decomposition, said hydrocarbonbeing selected from the group consisting of alkanes and mononucleararomatics containing only aromatic unsaturation.

2. The method of claim 1 wherein said hydrocarbon is an aromatic typesolvent having an initial boiling pointof about C. and a final boilingpoint of about C.

3. The method of claim 1 wherein said hydrocarbon is:

TOBIAS E. LEVOW,

H. M. S. SNEED, Assistant Examiner Primary Examiner

